Water treatment



WATERTREA'IMENT' Edwin D. Parsong 'fiartlesville, one. assignor to Phillips teiroleum Company, a corporation of Delaware Application August 19, 1953, Serial No. 3753105 r .16 cnn cuss-7 This invention relates to water treatment. In a further aspect this invention relates to a method for'secondary recovery of oil from oil bearing formations. In a further aspect this invention relates to particular treatment of the water which is returned tothe formation. In a further aspect this invention relates to a method for controlling Patented Mar. 26,. 1951 A further object of this'invention relates to a process for secondary oil recovery by water injection.

the sulfide ion concentration of water which is recovered with the oil by adding-an oxidizing agent, such as chlorine, to the water before returning it to the formation.

The use of water to reflood or pressure oil bearing forniations has come into wide use by the oil industry. In such opezation, the liquid from the well is separated to give an oil fraction and a water fraction. This water is then forced into the formation in order to make possible the recovery of further oil. This process, though quite simple in operation, has posed many new problems.

A further object of this invention relates to a method of -water treatment where water recovered with oil is jectcd into the formation.

A further object of this invention is to provide a web od for sulfide ion control to prcven'tprecipitation of undesirable materials in the injection wells of the reservoir.

Other objects and advantages of this invention will be ;apparent to one skilled in theart upon reading the accompanying disclosure.

I have inventeda process for water treatment which 'maltes possible control of thesulfide ion concentration to prevent undesirable precipitate formation. invention is illustrated in a modification applicable to the water flood- 1 ing of oil reservoirs. The process of this invention lies in my discovery that the sulfide ion concentration should be maintained between the limits of 0 and 2.5 parts per million, preferably less than 1.5 parts per million. In

other words, the sulfide ion concentration should be maintained low enough that ferrbus sulfides are not formed and this is done by addition of an oxidizing agent to the water. However, and equally important, an excess of the oxidi'zingagent should not be used. This is because these waters frequently contain ferrous compounds and themdition of' an excess of the oxidizing agent will-'convertsuch ferrous ions to the ferric state. The result is a forric hydroxide precipitate which is not removed by the til- One. of the most important of these problems is clogging of the formation as a result of materials WhlCh are m jected with the water into the ground.

It has been suggested that filters be used to removethese objectionable materials. Filters, however, are not the complete answer to the problem. Ferrous sulfide is one of the materials which has caused the greatest trouble.

' Even though the water removed from the oil may appear to be clear and colorless, the presence-of ferrous ions and sulfide ions will lead to the formation of t recipitate after a period of time. With one particular well, a sarnple of the water removed from the well becomes'gray' after standing about 30 minutes, and after standing-overnight a precipitate of black ferrous sulfide will be found.

on the bottom of a container. If such water is injected filters. Automatic means are provided for the introducinto a formation, the ferrous sulfide precipitate will plug the injection wells of the reservoir.-

Addition of an oxidizing agent to this water will oxidize the sulfide ion and prevent the formation of ferrous sul tide. However, simple addition of such an oxidizing agent is not the complete answer to the problem. If too much oxidizing agent is injected into the water stream, ferrous' ions will be oxidized to the ferric state. This-ferric iron then forms ferric hydroxide which is very diificult to remove by filtration ina closed system. j 7 Another possible solution to such. a'proolem, and one,

that is commonly used in water treatment, is the addition of an oxidizing agent, or simply aeration to oxidize sulfide ionsin the water. Using such a system with settling "tanks, there would be no problem if the oxidation were 'carried to a point where iron wasoxidized to the trivalent;

'stat"e- Large settlingtankscould be provided andthc water could be removed from these tanks by decantation and filtered. However, such a system is notdesirable in" a water injection process, mainly because'a large investment isrequired to construct and maintain the .water Each ofthc following objects is obtained by at leastohe of the aspects of thisinvention; v

An object of this invention relates methodnfand and apparatus forwater treatment.

ters and, in general, is very difficult to handle in a closed i system. p

Oxidizing agents preferred for-use in my invention are the halogens such as fluorine, chlorine and bromine and complexes thereof, i. e., a potassium iodide/iodine complex and the like. Chlorine, because of economic reasons and ease of handling, has been most used. In general, oxidizing agents are suitable if, as a resultof their use, no precipitates 'which will clog the formations are formed.

The process is relatively simple and the firststep comprises separating the water from the oil after it is re covered from the formation. After this separation, the oxidizing agent is added to the water upstream of the tion of thisoxidizing agent. Whenusing chlorine, it is introduced into a fresh water stream and this stream then contains hydrochloric acid and hypochlorous'acid. The-- amount of chlorine introduced is proportional to the amount of water flowing to the filters, this being con-' trolled by any. suitable means. A commercial venturi meter inserted in the line extending to the filters offers a simple method of determining and controlling the amount of chlorine to be added;

Following the chlorine introduction, the water is filtered to remove'suspended solids, such as corrosion products and insoluble precipitates formed upstream of the filters. After filtering, this water, with such additional water as is needed, is returned to the wells after'beingpressured to a suitable pressure. a I

The drawingjllustrates diagrammatically a closed re'- pressuring system employed in secondary recovery of oil from oil-bearing formations. '1 Referring now to the drawing, the fluid from the well comprising water and oil is conv'e'yed'through line 10 to an 1 oil-water separator, such as a heater treater 11, the opera tion of such apparatus being well known to those skilled in the art. If desired, a bactericide may be added through line 9. From this treater, oil is removed through line 12 and water is removed through lines 1; and 14 extending from the lower end portion of separator 11. This wafer flows through lines 16 to filters 1?, it being obvious that the number of filters required depends upon the size of I individual filters. 'It is preferable to use-more than one 1 The specific g ravitj' oi this water at 60 F..was 1.0318.

so that-one can be cleaned while maintaining flow 19'into line 16. Ihe water str'earn in line 19 is .rnadc up supplied through line 21 and chlorine.

offresh water through lineZZ. 7 1

' The amount of water containing chlorine injected into line 16 is controlled in response to liquid flow in water line 16 by means-of a flow meter 23, this being connected to chlorinator 18 by means of line 24. After passing through filter 17, the water is'convcyed to the injection wells through line 26, this stream being pressured to any Suitable pressure by means of pump 27. Fresh water, as needed, can be added to line 26 through conduit 28. Conduit 29 provides means for removing samples of the water contained in line 26.

In order to -further illustrate this invention, a series of tests were made on water obtained from the North Burbanlt Oil Field. The results of addition of different "amounts of chlorine is sct forth in the following table,

lowed to stand overnight,

is to be understood that all matter herein set forth,- or r the appearance being noted after the samples were aldioxide, at the end ofia 24 hour period.

'As manypossible embodiments may be made of invention without departing iron! the scope thereof, it

shown in theaccompanying drawing, is to be interpreted as illustrative and 'not as unduly limiting the invention.

lclaim:

l. A method of treating containing ferrous ions" and sulfide ions which com;tises adding an oxidizing agent to said water in an amount 'suflicient to maintain the concentration of said ions at less than 2.5 parts I per million, but insufficient to oxidize said ferrous ions.

2. A method of treating water containing ferrous ions and sulfide ions which comprises adding chlorineto said water in an amount suflicient to maintain the concentra- .tion of said sulfide ions at less :han 2.5 parts per million,

but insutficient to oxidize said ferrous ions.

ion concentration less than 15 parts per million.

4. The method-0f claim 2 in which chlorine is added in an amount sufficient to maintain the sulfide ion-com centration less than 1.5 para per million.

1 '5. In a'closcd system water repressuring method for I secondary recovery of oil from an oil-bearing formation,

' "Chlorine Dbsageln Appearance Final Solution, 11. p. m. v

0.3 Black ferrous sulfide on botlmn. 0.6 Do. 0.9 Do. 3.2.-- Do. i 1.8. Do. 1 '.4 170. 3.0.. Do. 41L. Do. I 2.8. No black ferrous sulfide. j

o. 10.0-. Nn hlncir terrors sulfide. but some red ferric hydroxlde present. '23. Red tloc 0t tm'rlc hydroxide. -47.0....... -Do.

.it will-be noted that the proper range is fairly narrow,

the correct chlorine dosage when dealing with this particular water sample being 6 to 8 parts per million.

' As will be obvious to those skilled in the art, a state ment of the amount of chlorine to be added means very. .little since it is dependent upon the sulfide ion concentration in the water. A particular water sample representative of water obtained from the North Burbank Oil Field has the following composition. v

Generally, the sulfide ion concentration is relatively i, v ...Table- .Componcnt: q l 7 Parts per-million Total solids 48,807

Sodium and potassium 14,637 {Zalciuni 3 ,395 Magnesium .541 Chloride 7 30,129 Bicarbonate Q Sulfate .24 Barium Y j y I 7 Sulfide Y I4 constant and does not vary greatly from day to day.

However, where this value does vary, automatic control means are necessary to increase the amount of osidizing agent'supplicd when the sulfide ion concentration increascs. For such operation, instruments for automatic dctermination of the oxidation-reduction potentialof the treated brine can be used to control the rate of addition of the oxiti'zing agent..

The filters used in the above described process'can be or any standard design and are usually filled with. coal Y or sand. When itisdesirabl-e. to clean them, this can he Ldone simply by hacltwashing. -Wher e a harlkef filters is The-simplest test to determine if the proper'amount of .used, tl*ea'sual process is to pass all of the water through part of thefilters'whilc the balance are being washed.

which method comprises sepzration of oil and water pro J duced from an oil-bearing formation, filtration of said water and injection of said water into an oil-bearingformation, andwherein said waier contains sulfide ions-and to maintain the concentration of said sulfide ions at less -than 2.5 parts per million, he: insufiicient to oxidizctsaid ferrous ions.

6. The process of claim 5 inwhich the amount of -oxidizing agent added is controlled automatically with respect to the water being fiizzred.

7. The method of claim 5 in which oxidizing agentisadded in an amount suflicicm to maintain the sulfide ion 1' concentration less than 1.5 parts per million.

8. A method of controlling sulfide ion concentration in "water which contains sulfide ions and ferrous ions so as to prevent the formation of inscuble ferrous sulfide-which comprises adding an oxidizing agent to said water in an a amount-sul'ficient to maintain concentration of said sulfide ions at less than 2.5 parts per million, but i-nsufficient tooxidize said ferrous ions.

91 A method according to claim 8 wherein said been ing agent is chlorine.

10. A method according to claim 8 wherein said ozidiz- I ing agent ishrominc.

ll. A method according todaintdwherein-sfld dxidizing agent is fluorine.

12. A method according to 33511 a i mid ing agent is a potassium iodid-e/iodine-complex.

13. A method of treating water containing both ferrous ionsand sulfide ions, which method comprises: measuring the concentration ofion in-the treated water;

addingan oxidizing agent to said water, and controlling,

the amount ofsaid-oxidizing agent addedto s'aid water ions and sulfide ions, which method comprises: addingnn agent to saidwater inan amount mlhcient to maintain the concentration oi said sulfide ion at lessthan ,2.$ parts-per million, said ant-mint ofoxidizing agent being -76 insufiicient torcduce thecomtmt-ion'of i- 1$. T'ne method of claim 14 wherein eaid oxidin'ngagentis chlorine. i

16; A closed system method of treating water which is i used as injection water-in secondary recovery of oil from anoil bearing formation and which water contains bOtil of water; adding an oxidizing agent to a second stream of References Cited'in the fiie of this patent UNITED snares PATENTS 1,100,675 Hacld et al; '3une 1.6, 1914 1,908,813 Schwab May 9, 1933 2,239,612 Lawlor -.---w-- Apr. 22, 1941 2,543.88 Stover i Mar. 6 1951 omen REFERENCES water in an amount proportional to the volume of said 10 --Tim Oil 5nd (388 30011181. July 2. 1945, pps. 157-158,

first stream of water, said amount being an amount sufficient to maintain the concentration of said sulfide ions at less than 2.5 parts per million, but insufficienl to oxidize said ferrous ions; combining said first. and said second streams of water to obtain a combined stream of water; 15 and filtering said combined stream of water.

Chemical treatment for oil-field water for injection into the ground. History of Water-Flooding of Oil Sand: in

U. S. Dept. of Interior, R. I. 3761,)l'uly, 1944,'pg. 42.

The Oil Weekly, April 2, 1945, pps. 40, 42,-44, 46, 81!

48, .Water flooding in Oklahoma. 

5. IN A CLOSED SYSTEM WATER REPRESSURING METHOD FOR SECONDARY RECOVERY OF OIL FROM AN OIL-BEARING FORMATION, WHICH METHOD COMPRISES, SEPARATION OF OIL AND WATER PRODUCED FROM AN OIL-BEARING FORMATION, FILTRATION OF SAID WATER AND INJECTION OF SAID WATER INTO AN OIL-BEARING FORMATION, AND WHEREIN SAID WATER CONTAINS SULFIDE IONS AND FERROUS IONS, THE IMPROVEMENT WHICH COMPRISES; ADDING AN OXIDIZING AGENT TO SAID WATER PRIOR TO SAID FILTRATION, SAID OXIDIZING AGENT BEING ADDED IN AN AMOUNT SUFFICIENT TO MAINTAIN THE CONCENTRATION OF SAID SULFIDE IONS AT LESS THAN 2.5 PARTS PER MILLION, BUT INSUFFICIENT TO OXIDIZE SAID FERROUS IONS. 